1. Field of the Invention
The present invention relates to an image forming apparatus that adopts an electrophotographic scheme or an electrostatic recording scheme.
2. Description of the Related Art
Generally, there are tandem type and rotary type color (multicolor) image forming apparatus that adopt an electrophotographic scheme or an electrostatic recording scheme. With the tandem type apparatus, before an intermediate transfer belt makes one full rotation, a toner image is formed on the intermediate transfer belt by a plurality of image forming units each of which is provided with a photosensitive drum (Japanese Patent Laid-Open No. 2000-351472). On the other hand, with the rotary type apparatus, a single photosensitive drum is shared by a development rotary provided with developers corresponding to plural colors, and an intermediate transfer belt is caused to make a plurality of full rotations, thereby forming a multicolor toner image on the intermediate transfer belt (Japanese Patent Laid-Open No. 2004-37916).
In particular, with the rotary type apparatus, a toner image is formed on the intermediate transfer belt, and thereafter feeding of a transfer material starts. Thus, if feeding of a transfer material fails, the toner image formed on the intermediate transfer belt cannot be transferred to a transfer material, which wastes toner.
Note that with both the tandem type apparatus and the rotary type apparatus, secondary transfer of a toner image can be performed at a desired position on a transfer material by matching the timing at which the toner image arrives at a secondary transfer position and the timing at which the transfer material arrives there. However, if a resist roller, which adjusts the timing at which the transfer material is conveyed in order to adjust the arrival timing of the transfer material, deteriorates, there are cases where the timing at which the transfer material arrives at a transfer position comes after the desired timing. Japanese Patent Laid-Open No. 2000-351472 discloses that the timing of resuming the conveyance of a transfer material, and its conveying speed are adjusted using a resist roller. Japanese Patent Laid-Open No. 2004-37916 discloses that the rotational speed of the intermediate transfer belt is adjusted.
However, in both of the inventions disclosed in Japanese Patent Laid-Open No. 2000-351472 and Japanese Patent Laid-Open No. 2004-37916, it is assumed that a transfer material is conveyed normally to the resist roller. Therefore, it is not possible to cope with the difference in the timing at which a transfer material reaches the resist roller that occurs because of the fall of the conveying capability of a pickup roller due to change with time, wear, and the like, the type and quality of the transfer material, and so on. Further, if the transfer material is not conveyed to the resist roller, a toner image cannot even be transferred. In this case, the toner image that is carried on the intermediate transfer belt is cleaned and discarded, and thus toner is consumed wastefully.